The present invention relates to equipment used for chemical vapor deposition (CVD) plasma enhanced chemical vapor deposition (PECVD) and reactive ion etching (RIE), and more particularly to gas distribution heads utilized in such equipment.
Gas distribution heads, or showerheads as they are sometimes known, are utilized in deposition and etching systems such as, for example, plasma enhanced chemical vapor deposition (PECVD) systems and reactive ion etching (RIE) systems. A schematic representation, in cross section, of such a showerhead is shown in FIG. 1. The showerhead, generally designated 100, includes an outer casing 102 which surrounds an internal plenum 104. A plurality of apertures 106 are formed in a gas outlet portion of the casing 102. A silicon substrate 108, used in fabrication of integrated circuits, is placed on a platen 110. The platen 110 is positioned with respect to the showerhead 100 such that the substrate 108 is situated in proximity to the apertures 106 in the gas outlet portion of the casing 102.
In both the deposition and etching processes, a gas or gas mixture flows into the plenum 104 and out of the apertures 106 toward the surface of the substrate 108. The platen 110 is maintained at a predetermined temperature and predetermined electrical potential with respect to the gas distribution head 100. The platen 110 maintains the substrate 108 at a predetermined temperature. The substrate 108, being electrically connected to the platen 110, is also maintained at the same electrical potential as the platen 110 with respect to the gas distribution head 100. This electrical potential is typically a radio frequency (RF) potential applied between the gas distribution head 100 and the platen 110. In a deposition process, for example a PECVD process, silane (SiH.sub.4) and oxygen (O.sub.2) gases flow into the gas distribution head 100 through the plenum 104 and out of the apertures 106. Because of the temperature at which the wafer is maintained, and the potential difference between the electrode and substrate 108 on the one hand and the gas distribution head 100 on the other hand, the silane and oxygen gases react to form a glass (SiO.sub.2) on the surface of the substrate 108.
In an etching process, such as an RIE process for etching a layer of aluminum disposed on the substrate 108 into a pattern of interconnects, a gas, such as chlorine, flows into the gas distribution head 100, through the plenum 104 and out of the apertures 106 toward the substrate 108. The aluminum layer disposed on the substrate is coated with a predetermined pattern of protective resist. The protective resist which remains on the aluminum layer defines the interconnect pattern. The potential difference maintained between the substrate 108 and the casing 102 of the gas distribution head 100 causes the chlorine gas to ionize and react with exposed portions of aluminum on the surface of the substrate 108 (i.e., those portions not covered by the protective resist) to form a volatile material, aluminum chloride (AlCl.sub.3), which is carried away leaving the protected aluminum as the unetched remainder. In this case, the chlorine is directionally accelerated into the surface of the wafer to generate an anisotropic etch profile.
In both the above processes, particles are transported or formed in the showerhead which may attach to the inner walls of the casing 102 and/or flow toward the apertures 106. Those particles flowing through the apertures could undesirably mask portions of the surface and cause functional defects on the die in the wafers. Other particles may tend to accumulate and ultimately clog one or more of the apertures. Clogging of the apertures 106 necessitates either replacement of the gas distribution head 100 or its removal and cleaning. Both of these operations are very expensive in terms of time and wafer through put. Therefore, it is desirable to provide an improved gas distribution head which would facilitate the removal of particulates formed within the head, thus reducing the number of wafer defects and preventing the obstruction of apertures in the gas distribution head caused by such particles.